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Abstract:

Abstract Supermassive black hole (SMBH) masses can be measured using molecular gas kinematics. Here we present high angular resolution (0.12 arcsec or ≈11 pc) Atacama Large Millimeter/submillimeter Array observations of the 12CO(2–1) line emission of the early-type galaxy NGC 1387. The observations reveal a face-on, regularly-rotating central molecular gas disc with a diameter of ≈18 arcsec (≈1.7 kpc) and a central depression slightly larger than the SMBH sphere of influence. We forward model the CO data cube in a Bayesian framework with the Kinematic Molecular Simulation code, and use Hubble Space Telescope data to constrain the stellar gravitational potential contribution to the molecular gas kinematics. We infer a SMBH mass of $1.10^{+1.71}_{-0.95}[\textrm{stat},3\sigma ]^{+2.45}_{-1.09}[\textrm{sys}]\times 10^8$ M⊙ and a F160W-filter stellar mass-to-light ratio of $0.90^{+0.44}_{-0.35}[\textrm{stat}, 3\sigma ]^{+0.46}_{-0.36}[\textrm{sys}]$ M⊙/L⊙, F160W. This SMBH mass is consistent with the SMBH mass – stellar velocity dispersion relation.

Abstract:

Molecular gas is crucial to understanding star formation and galaxy evolution, but the giant molecular clouds (GMCs) of early-type galaxies (ETGs) have rarely been studied. Here, we present analyses of the spatially resolved GMCs of the lenticular galaxy NGC 1387, exploiting high spatial resolution ( or 14 pc) CO(2-1) line observations from the Atacama Large Millimeter/submillimeter Array. We identify 1285 individual GMCs and measure the fundamental properties (radius, velocity dispersion, and molecular gas mass) of each with a modified version of the CPROPStoo package. Unusually for an ETG, the GMCs of NGC 1387 follow scaling relations very similar to those of the Milky Way disc and Local Group galaxy clouds, and most are virialized. GMCs with large masses and radii and/or small galactocentric distances have their angular momenta aligned with the large-scale galactic rotation, while other GMCs do not. These results show that ETGs have more diversified GMC properties than previously thought. We discuss potential reasons for such diversity, and viewing-angle dependency is a plausible candidate.